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题名:
Web应用服务器关键技术研究
作者: 范国闯
答辩日期: 2004
专业: 计算机软件与理论
授予单位: 中国科学院软件研究所
授予地点: 中国科学院软件研究所
学位: 博士
关键词: Web应用服务器 ; 动态可重配模型 ; 多层次可重配体系结构 ; 自适应负载平衡 ; 反射式组件容器 ; 组件动态分布
其他题名: Research on Some Key Technologies for Web Application Servers
摘要: 随着因特网迅速发展,网络软件平台已成为当今软件技术发展主流趋势和竞争焦点,其核心和关键是位于中间层的Web应用服务器。Web应用服务器是在Web计算环境下产生的一种新型中间件,为创建、部署、运行、集成和管理Web应用提供名字解析、负载平衡、事务控制、失效恢复、容错、安全等一系列运行时基础服务,并具有高可伸缩性、高可用性、高可靠性和高效等特性。它屏蔽了底层操作系统的差异,为大型网络化应用系统提供运行支撑环境,降低软件复杂度和难度,避免重复劳动,提高可重用程度,加快软件开发的进度,提高软件开发的成功率和软件质量,并大大降低了软件的维护难度。Web应用服务器具有良好的应用前景,可广泛应用于企业信息化、电子商务、电子政务等领域。Veb应用服务器自产生以来,得到工业界和学术界的普遍关注,已成为最近几年最热门的软件类型,被认为是自从关系型数据库以来最令人激动的企业应用技术。针对Web应用这一主流发展趋势以及Web应用服务器的软件基础设施作用,本文选择Web应用服务器的重要关键技术问题进行研究,并将这些问题的解决办法和技术应用到我们自主研制的JZEE应用服务器。鉴Web应用服务器在网络软件平台中的作用和地位,国际上诸多著名IT企业纷纷推出其各自的产品和系统。目前主流、Veb应用服务器都是这些国外产品,迫切需要研究和开发具有自主知识产权的Web应用服务器。论文对We应用服务器的研究热点和关键技术的现状进行分析。虽然Web应用服务器已逐步成熟,但由于大多数均采用一体化体系结构和黑盒抽象机制进行设计,还存在开放性和灵活性差、可定制性差、便利性和自适应能力低以及客户透明性不强等不足之处。为了满足Web计算动态性所带来的不断变化的需求,Web应用服务器需具备在运行期间可动态重配的能力。论文建立了Web b应用服务器的动态重配模型OllceDR,并设计了一种动态重配算法,驱使系统逐步进入重配安全状态,从而维持系统重配前后的结构完整性、交互状态和应用状态的一致性。基于反射中间件技术,结合微内核技术和组件技术,设计覆盖\V已b应用服务器整个生命周期的多层次重配体系结构。该体系结构支持OllceDR模型,具有较好的可扩展性、灵活性和开放性。论文提出一个复合元对·象的EJB容器厅射才草刑.捅付陌珊枯*立孤△np机制,设计一种在运行期间动态编排 AsPect调整自身行为的组件容器OnceAOc。Ollce AOP具有针对性强、动态自适应性好和透明性高等特点。此外,将容器与通信方式分离,采用客户端动态代理技术,OnceAOC具备根据系统运行时状态选择最优的通信方式的能力,支持进程内和主机内两种分配优化。针对认Web应用服务器负载平衡服务的特殊需求,论文设计了一种基于中间件的自适应负载平衡服务,阐述实现该服务的若干关键技术及其解决办法,包括可热插拔、负载策略可替换、负载反馈与自适应控制、状态迁移以及容错技术等。此外,结合发送者启动和接收者启动算法的优点,设计了一种非精确、主动式自适应算法,该算法允许各处理器间负载有差别的情况下,发送者和接收者都主动注册自身的负载状态。不管是低负载情况还是高负载情况,调度者都能快速配对接收者和发送者,算法具有适用面广、配对快速、稳定性较高等特点。静态分布不能满足Web应用对组件进行动态布局的要求。为此,论文讨论并重点解决如何在J2EE应用服务器中对EJB组件进行动态分布和迁移。定义了E.IB组件迁移模型及其相应的迁移原语和约束,并针对各类组件类型的特点,设计了SLB_Copy、sFB_ copy、EB_copy三个组件迁移算法。算法已应用到自适应负载平衡、失效恢复以及、Web应用的动态重配等三个方面。上述若干关键问题的解决方案和技术崇山峻已应用服务器OnceASZ中实现。目前,OnceAS已通过了SUNJPS的所有功能测试,支持2J2EEI.3规范,并通过了JZEE应用服务器性能测试基准ECperf 要求的各项性能指标。
英文摘要: With the explosive development of Internet, software platforms for Web applications have been the mainstream category in software industry.The core and key element of the platform is Web Application Server(WAS),which resides at the middle tier in the three-tier client/server architecture.WAS solves the problems in applying traditional middlewares to Web computing environment and provides a series of run-time services such as naming, load balancing,transaction,failover,fault tolerance and security, to support for the deployment, integration, and execution of Web applications.High scalability,availability, reliability, and performance are the advanced features of WASs. WAS has a huge potential market, and it can be used to to build enterprise management system, e-commerce, and e-government system. Attention to the new category of middleware has been drawn from the academia and software industry after it was born inl998. It is considered to be one of the most exciting milestones of enterprise software technology since the relational database and has become very popular in the last few years. To meet the urgent need for WAS and cater for the mainstream trend of Web applications, this thesis outlines some key issues in developing WAS, and their solutions are applied to design and implement J2EE application server. Many international IT companies have released their WAS product, and have become mainstream WAS product providers. The fact makes it necessaiy to develope WAS whose copyright is reserved for our country. In this dissertation, the current state-of-the-art of Web application servers is outlined. We come to the conclusion that support for openness, flexibility, customizability, portability, and client transparency is not available in the current mainstream WASs,which typically adopt a monolithic architecture and inherent black box philosophy to their design. A comparative study among some leading Web application servers is presented by evaluating their functions and performance. To cater for an increasingly diverse range of QoS demands, a dynamic reconfiguration model for WASs, referred to as OnceDR, is presented, and a run-time reconfiguration algorithm is designed to drive the system to be reconfiguration-safe state for the purpose of preserving the reconfiguration consistency. A multi-phase reconfigurable architecture is introduced on the base of OnceDR model, supplemented by the marriage of microkernel technology and reflection technology. In the architecute, WAS is very open and flexible to support deployment-time configurability and run-time reconfigurability. A reflective container model for EJB components is proposed. In this model multiple meta-objects are composed to represent the functionality of an EJB component. The AOP technology is introduced to the design of containers, and an AOP mechanism is implemented via reflection. OnceAOC is designed.The container can be capable of adapting their behavior to the changing environments though dynamically weaving multiple aspects at run-time.Process-collocation and host-collocation is supported to improve the performance of communication in OnceAOC. To improve the dependability and scalability of WASs, a middleware-based adaptive load balancing service is designed. We also describe the key design challenges including hot plug-in, customizable load balancing strategy, adaptive control, state migration and fault tolerance etc., and outline the technical solutions.Moreover, a fuzzy and positive load balancing algorithm is also proposed with combination the advantages of both sender-initiated algorithm and receiver-initiated algorithm.The adaptive algorithm is charactered by quick matching and stability. The most challenging problem is to maintain component consistency during component dynamic redistribution. To resolve this inconsistency problem, some kinds of component migration constrains (CMC) are defined basically. A component migration model for J2EE application servers is proposed, and SLB_Copy, SFB_Copy and EB_Copy component migration algorithms are presented. It is proved that SLB_Copy, SFB_Copy and EB_Copy migration algorithms all satisfy the CMC constrains. These algorithms are applied to provide many services such as the adaptive load balancing service and the failover service. A J2EE application server, referred to as Once AS, is implemented. The approaches and solutions the thesis proposed are applied to the design and implementation of OnceAS. At present, OnceAS has passed all the test cases in Sun PetStore test suite. All the stressing test cases in ECPerf benchmark have been passed also. OnceAS can be used widely in small and middle-sized enterprises.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.iscas.ac.cn/handle/311060/6412
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Recommended Citation:
范国闯. Web应用服务器关键技术研究[D]. 中国科学院软件研究所. 中国科学院软件研究所. 2004-01-01.
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